Computational and experimental analysis of the mechanical performance of SLS generated polymer-ceramic bone scaffold materials
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The load-bearing ability of orthopaedic scaffolds in critical-sized defects is of critical importance. 3D printing methods such as selective laser sintering (SLS) have great potential for the fabrication of patient-specific scaffolds. The incorporation of ceramic particles is desirable to promote osteogenesis; however the influence of these particles on the microstructure and mechanical behaviour of SLS materials is unclear. A multiscale modelling methodology is developed to predict the macroscale elastic properties of polymer-ceramic SLS materials with complex microstructures. The relationship between micromechanics-evaluated elastic properties and average grey-value is found to be material-specific. The macroscale elastic modulus of SLS materials with different volumes of beta-TCP particles is accurately predicted when element-specific assignment of elastic properties based on grey-value is used. Increasing the ceramic content of these SLS materials is shown to result in a slight increase in stiffness but significant reductions in strength. Changes in mechanical properties under simulated physiological degradation conditions are evaluated, and are shown to be dependent on the incorporation of ceramic particles. Computational models of critical-sized ovine tibial defects with implanted scaffolds are generated. The ability of each defect to withstand bending and compressive loading is analysed, demonstrating the influence of callus volume and of both scaffold volume and stiffness on defect load-bearing. Clinically-used metrics for the prediction of the safety of removing external fixation are evaluated for each defect and deficiencies in these measurements are demonstrated by comparison with simulation results. In conclusion, the use of both mechanical testing methods and computational modelling in this thesis has led to an improved understanding of the influence of ceramic content on mechanical properties as well as the development of a multiscale modelling methodology to prediction macroscale mechanical properties. Computational modelling of real defect geometries has resulted in a non-invasive method to assess defect stability and load-bearing capacity.
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